How animals are useful in drug development?

Before any drug is tested on humans it has to be tested on animals.

As a preliminary study, companies test the effect of new chemicals on animals. After the new chemical passes safety and efficacy standards then companies obtain permission from food and drug administration (FDA) for testing the effect of chemical on interested human subjects.   

FDA (and/ other relevant authorities) scrutinize the data of animal study to analyse the beneficial effect of new chemical on animals. After FDA is satisfied with the data then it permit to test chemicals on humans as per set standards and protocols. 

Suppose a company wants to market a new medicine to treat diabetes. It select a suitable animal model of mice/rat, and induce diabetes by administering streptozotocin and then administer new chemical to test if it decreases blood sugar. Some time isolated animal tissues are also helpful to test the effect of new chemical. When FDA is satisfied with the fact that new chemical decrease blood sugar level and safe to animal, FDA permits to test the effect of new chemicals on healthy and diabetes patients. If the new chemical meets safety and efficacy standard then company gets FDA nod to market it and now the new chemical becomes a medicine.

For science research, animal study protocol need to be approved by ethics committee. Animals are treated humanly and are maintained under standard laboratory conditions (room temperature, suitable humidity,  environment with minimal noise, sufficient food and water). 

References:

1. Mark Mathieu. New Drug Development: A regulatory overview. Parexel Intl Corp. 

2. Goswami SK, Manikanta V, Suma KG, Razdan R, Inmadar MN. Efficacy of Ellagic acid and sildenafil in Diabetes induced sexual dysfunction. Pharmacog Mag 2014; 10(Suppl S3): 581-7. 

3. Goswami SK, Inamdar MN. Screening of new compounds for the management of erectile dysfunction. J Young Pharm 2014; 6(4):51-55.